Before this we'd just exit(0) and let the OS clean up after us, but
e.g. with post-buffering=1 we'll end up with a temporary file in /tmp
that we won't clean up when we exit unless DESTROY is called.
This resulted in us leaking files in /tmp if we ever had a request where
the last request before a harakiri was a POST request with a body we'd
buffer to /tmp.
We'd have similar leaks in any user-defined code that required DESTROY
to run.
Aside from this I'm still not very comfortable with what this whole code
here in psgi_plugin.c and psgi_loader.c is doing when managing the
interpreter(s). It:
* Doesn't consistently call PERL_SET_CONTEXT() as described in "perldoc
perlembed".
* Nothing calls PERL_SYS_TERM() either.
* Should we be calling uwsgi_perl_free_stashes() here too?
To test this:
UWSGI_PROFILE=psgi python uwsgiconfig.py --build
./uwsgi --master --http-socket localhost:1234 --psgi t/perl/test_harakiri.psgi
Then elsewhere:
curl 'localhost:1234?0'
curl 'localhost:1234?1'
Both of those should emit "Calling DESTROY".
It can be reproduced by enabling the Perl debugger inside a PSGI application:
{
package DB;
sub DB { }
sub sub { &$sub }
}
$^P = 0x73f;
sub { [200, ['Content-Type' => 'text/plain'], ['Hello World']] }
For every request the following warnings are emitted:
Attempt to free unreferenced scalar: SV 0xfea6e8, Perl interpreter: 0xd534a0.
Attempt to free unreferenced scalar: SV 0xfea718, Perl interpreter: 0xd534a0.
where the unreferenced scalars are the uwsgi::input/uwsgi::error instances
created in build_psgi_env.
The calling convention for Perl subroutines is that the values pushed on the
stack must be mortalized in the callee, and if the caller wants to retain them,
it must do a SvREFCNT_inc to undo the effect of the mortalization.
Before this patch XS_input/XS_error were not mortalizing the value, and
uwsgi_perl_obj_new was not incrementing the reference count, so the two bugs
balanced each other.
When running under debugger, Perl forwards all function/method calls to
DB::sub, which causes a mortal copy of the return value of
uwsgi::input/error::new to be pushed on the stack. The value is cleared by the
FREETMPS at the end of uwsgi_perl_obj_new, and the freed value is added to the
environment hash. The warning is emitted at the end of the request when the
environment hash is freed and Perl notices that some of the values has been
already freed.
newRV(sv_newmortal()) is equivalent to newRV_noinc(newSV(0)): the former
creates a new SV with refcount 1, schedules a decrement "soon" (the
mortalization) and increments the refcount, the net result is a refcount of 1,
which is what the latter does.
Unbit